2
6
27
2.3c
Power Combiner:
Schematic Diagram 10394221/Rev 51
t
A3CP2
Insertion Loss (J1-J2 & J3)
3.25dB
Frequency
470-806MHz
The Power Combiner is a standard Wilkinson circuit that combines the two amplified signals from
the 300 Watt Power Amplifier assemblies (A1, A2). The recombined signal is then brought to the
drawer’s output connector and applied to the UHF Bandpass Filter (A7FL1) located in the
transmitter Output Section.
2.3d
Amplifier Status Interface:
Schematic Diagram 20394216/Rev 53
t
A3PC1
The Amplifier Status Interface board monitors two critical areas in the 500 Watt Power Amplifier
drawer: the 32V Power Supply outputs and the 300W Amplifier operational status. The Status
board receives power from the two 32V Power Supplies (PS1/PS2) within the amplifier drawer
through inputs J1-1 & 2 and diodes CR1/CR2. Voltage divider resistors R4/R5 provide a 14V
reference at pins U1A-3/U1B-5 which, assuming both power supplies are operating properly, are
compared to the 16V inputs present at U1A-2/U1B-6 via dividers R2/R3 and R1/R6. In this
situation, output pins U1-1 & 7 are negative forcing U2B-7 positive and forward biasing Q1A. The
ground appearing at J1-3 is relayed to the Control/Monitor board (A5PC1) illuminating the POWER
SUPPLY LED on the transmitter’s Control/Metering panel via A3J3-6 and A5PC1J1-6/A5PC1J2-6.
If either one of the power supply outputs drops below 28V, U1A-1/U1B-7 will turn positive, creating
a negative at the base of Q1A through U2B, shutting off the Control/Metering POWER SUPPLY
indicator. Concurrently, a low will be sent to the IF/Converter Output AGC Control (PC1J6-10)
from the Control/Metering panel, disabling the circuit so that the transmitter can continue to operate
at a lower power.
The second function of this board is to monitor the operation of each 300 Watt Power Amplifier
assembly. When operating properly, low voltages are forwarded from the amplifier transistor
output monitor circuits at A1TB1-4/A2TB1-4 to J1-5/J1-6. Comparator U2A will supply a low at
pin 1 keeping control transistor Q1B reverse biased, FAULT OUT line J1-4 high and Control/
Metering AMPLIFIER indicator (A5PC1DS1) lit. If a transistor in one of the 300W Amplifier’s
happens to fail, a high will be generated at either A1TB1-4 or A2TB1-4 and at J1-5 or J1-6, pushing
the output of U2A high and biasing transistor Q1B into conduction. The short created at J1-4 will
extinguish the AMPLIFIER indicator located on the transmitter’s Control/Metering panel. As before,
a low will be sent to the IF/Converter Output AGC Control line (PC1J6-10) from the Control/
Metering panel, disabling the AGC circuit so that the transmitter will continue to operate at reduced
power.
2.3e
Power Supply/Thermal Interface:
Schematic Diagram 30400055/Rev 52
t
A3PC2
The purpose of the Power Supply/Thermal Interface board is to monitor the thermostats (A1S1/
A2S1) on each 300 Watt Amplifier assembly and activate the associated power supply if the